A key concern of the '90's is how to preserve the environment. Preservation efforts include the elimination or detoxification of effluents, including waste water from photographic processors. Conventionally, large baths are used by such processors, which contain chemicals of various toxic types to develop photographic images. Such excess aqueous solutions have only two options for disposal--either they have to be constantly reused (to avoid disposal entirely), or they have to be disposed of in a way that is not harmful to the environment. The former solution has the disadvantages of requiring constant adjustments to the chemical concentrations to deal with depletion of desired chemicals and the possible buildup of, or contamination from, undesired chemicals. For example, the use of baths of excess developer solution means that if subsequent stations are used for a treatment of continuous streams of photographic product, each at a different concentration, there is a risk of cross-contamination as the product moves from one station to another. The alternative of dumping a contaminated bath in favor of a fresh batch has the disadvantages of requiring removal of the noxious chemicals, if possible, prior to dumping, or contamination of the environment, if not possible.
Such disadvantages could be obviated entirely if excess developer solutions could be avoided. Although such an approach suggests as a solution, using only the amount of developer solution needed to swell and develop a given print, and no more, it has not been possible to apply such an amount of effluent-free developer to photographic material using conventional coaters. As used herein, "effluent-free" means free of liquid effluent, since the swelling of the gelatin has to be reduced by removing the water in a heater as vapor. However, such a gaseous effluent is less harmful than liquid effluents. That is, conventional coaters typically apply a continuous stream that exceeds in volume and rate that which the underlying support can absorb, so that there are fewer demands on the coater. However, if the liquid to be coated is delivered only at the volume and at a rate that can be absorbed for development purposes, the coater has to be able to stop and start intermittently, and at the same time produce a liquid wavefront that is controlled and of uniform width, depth, and length. Such a coating operation has not been possible using coaters of the prior art. Furthermore, to be commercially viable, the coater must be able to be mass produced, preferably of injection molded plastic, and require minimum operator attention to function properly. This means that the effectiveness of the coater must not depend on machining tolerances that are unrealized by traditional techniques for fabricating injection molded parts (tolerances of less than 0.005").
Finally, it has been suggested in the past that a liquid effluent-free process of development is possible if one sprays developer onto the photographic product. See, e.g., Canadian Patent 663,837. The problem with spraying is that a fine mist, high pressure spray produces a saturating mist of caustic pH that is itself intolerable. A low pressure, coarse mist spray avoids this problem, but fails to produce a coating that is sufficiently uniform.
Hence, prior to this invention it has not been possible to provide a method of effluent-free developing of a photographic product using only the volume and rate of liquid that can be absorbed by that product during development, e.g., from about 5.0 to about 100 mL/m.sup.2 over about 30 sec., since no coater was available that had this capability. (As noted above, "effluent-free" as used in this application refers to freedom from significant liquid effluent, that is from amounts of liquid effluent that have to be disposed of in ways that risk contamination of the environment. Any coater that inadvertently leaves a few drops of developer behind is not considered to produce "significant" liquid effluent.)